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DOI: 10.1122/1.4997587
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We study the fracture of reversible double transient networks, constituted of water suspensions of entangled surfactant wormlike micelles reversibly linked by various amounts of telechelic polymers. We provide a state diagram that delineates the regime of fracture without necking of the filament from the regime where no fracture or break-up has been observed. We show that filaments fracture when stretched at a rate larger than the inverse of the slowest relaxation time of the networks. We quantitatively demonstrate that dissipation processes are not relevant in our experimental conditions and that, depending on the density of nodes in the networks, fracture occurs in the linear viscoelastic regime or in a non-linear regime. In addition, analysis of the crack opening profiles indicates deviations from a parabolic shape close to the crack tip for weakly connected networks. We demonstrate a direct correlation between the amplitude of the deviation from the parabolic shape and the amount of non linear viscoelasticity.

Commentaires: . Réf Journal: Journal of Rheology 61(6), 1267-1275, 2017

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Ref Arxiv: 1706.04112
DOI: 10.1103/PhysRevLett.119.205501
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31 Citations
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Marginally stable solids have peculiar physical properties that were discovered and analyzed in the context of the jamming transition. We theoretically investigate the existence of marginal stability in a prototypical model for structural glass-formers, combining analytical calculations in infinite dimensions to computer simulations in three dimensions. While mean-field theory predicts the existence of a Gardner phase transition towards a marginally stable glass phase at low temperatures, simulations show no hint of diverging timescales or lengthscales, but reveal instead the presence of sparse localized defects. Our results suggest that the Gardner transition is deeply affected by finite dimensional fluctuations, and raise issues about the relevance of marginal stability in structural glasses far away from jamming.

Commentaires: 5 pages, 3 figures. Réf Journal: Phys. Rev. Lett. 119, 205501 (2017)

Ref HAL: hal-01539472_v1
DOI: 10.1051/epjconf/201714008013
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Wheat grains can be considered as a natural cemented granular material. They are milled under highforces to produce food products such as flour. The major part of the grain is the so-called starchy endosperm.It contains stiff starch granules, which show a multi-modal size distribution, and a softer protein matrix thatsurrounds the granules. Experimental milling studies and numerical simulations are going hand in hand tobetter understand the fragmentation behavior of this biological material and to improve milling performance.We present a numerical study of the effect of granule size distribution on the strength of such a cementedgranular material. Samples of bi-modal starch granule size distribution were created and submitted to uniaxialtension, using a peridynamics method. We show that, when compared to the effects of starch-protein interfaceadhesion and voids, the granule size distribution has a limited effect on the samples’ yield stress.

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L’encapsulation de molécules pi-conjuguées dans la cavité de nanotubes de carbone monofeuillets permet l’élaboration de nano-systèmes hybrides aux propriétés optoélectroniques modulables. Cette étude concerne le confinement de quaterthiophene dans des nanotubes de différents diamètres. Les interactions physiques entre les chromophores confinées et les nanotubes hôtes sont étudiées par spectroscopies de photoluminescence (PL) et de diffusion Raman. Les mesures de PL montrent une amélioration importante de l'intensité de photoluminescence (facteur 5) pour les nanotubes de faibles diamètres (0.9 nm). Les modes Raman haute fréquence (bande G autour de 1600 cm-1) des systèmes hybrides présentent une baisse d'intensité associée à des modifications de profil et de position. Ces différents comportements sont compatibles avec un transfert d'électrons de la molécule vers le nanotube. De plus, proche de l’énergie d’absorption de la molécule confinée, les effets sur la bande G sont amplifiés, suggérant fortement un transfert d'électrons photo-induit. Enfin, le profil Breit-Wigner-Fano (caractéristique du couplage électron-phonon dans les nanotubes métalliques) de la bande G est fortement affecté pour les nanotubes métalliques fonctionnalisés en surface, ce qui traduit un affaiblissement du couplage électron-phonon. Après encapsulation du quaterthiophene, ce profil particulier est retrouvé, ce qui suggère fortement un renforcement du couplage. Ainsi, le confinement de molécules pi-conjuguées dans les nanotubes de carbone permet de déplacer le niveau de Fermi du nanotube et, par conséquent, de moduler les propriétés opto-électroniques.

Ref HAL: hal-01632358_v1
DOI: 10.1038/nature23656
WoS: WOS:000410555900041
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Although ferromagnets have many applications, their large magnetization and the resulting energy cost for switching magnetic moments bring into question their suitability for reliable low-power spintronic devices. Non-collinear antiferromagnetic systems do not suffer from this problem, and often have extra functionalities: non-collinear spin order may break space- inversion symmetry and thus allow electric-field control of magnetism or may produce emergent spin–orbit effects that enable efficient spin–charge interconversion. To harness these traits for next-generation spintronics, the nanoscale control and imaging capabilities that are now routine for ferromagnets must be developed for antiferromagnetic systems. Here, using a non-invasive, scanning single-spin magnetometer based on a nitrogen–vacancy defect in diamond, we demonstrate real- space visualization of non-collinear antiferromagnetic order in a magnetic thin film at room temperature. We image the spin cycloid of a multiferroic bismuth ferrite (BiFeO3) thin film and extract a period of about 70 nanometres, consistent with values determined by macroscopic diffraction. In addition, we take advantage of the magnetoelectric coupling present in BiFeO$_3$ to manipulate the cycloid propagation direction by an electric field. Besides highlighting the potential of nitrogen–vacancy magnetometry for imaging complex antiferromagnetic orders at the nanoscale, these results demonstrate how BiFeO$_3$ can be used in the design of reconfigurable nanoscale spin textures.

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Our project is focused on the development of a continuous encapsulation process based on the crossing of an interface by droplets of an active ingredient that have to be encapsulated. The aqueous drops are injected in an organic phase, and as the system rotates each drop is driven outwards until it reaches the interface. Under adequate conditions, it crosses the interface and at a high inertia it drives a volume of organic phase which constitutes the coating

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In this paper we present geometrical measurements made on aqueous polyacrylamide gels withlab-based micro-tomography, one of the most convenient ways of accessing a quantitative measurement of thefascinating shapes that these materials make when hanging under their own weight.